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HIGH VELOCITY OXY FUEL SPRAY COATINGS FOR WEAR AND HOT CORROSION PROTECTION
Materials operating at high temperatures fail due to erosion-corrosion, wear, oxidation, and hot corrosion. In the recent years, there has been a growing interest in the use of thermal spray coatings onto the surfaces of engineering components to allow them to function under extreme conditions. Among the available HVOF process provides the coatings with have high density, increased thickness capability, smoother surface finish, lower oxide levels, low porosities, less effect of the environment during the spray process and have better corrosion and wear resistance properties. This study is done with the aim of putting together the performance capabilities and applications of HVOF process.
Surface and Coatings Technology, 2006
The minimization of cost and the enhancement of reliability of rotating and stationary fluid machinery equipment that are subjected to highly erosive and corrosive environments is mandatory in the oil and gas production industries. This can be achieved by minimizing the material damage resulting from the combination of solid particle impingement and corrosion. The high velocity oxy-fuel (HVOF) process is one method of producing metallic coatings to protect metallic surfaces from high temperature, wear, and corrosive environments. Stainless steel components coated with Inconel-625 are very common in the oil/gas industry. In this study, the erosion-corrosion characteristics of HVOF thermally sprayed Inconel-625 powder coatings were evaluated when applied on three different metallic surfaces: (a) plain stainless steel (SS), (b) spot-welded stainless steel (SW-SS), and (c) a composite surface of stainless steel and carbon steel welded together (C-SS-CS). These coated surfaces were tested in a jet impingement rig under two fluid conditions: (i) free from added solids, (ii) containing 1% silica sand. Weight loss measurements were used to provide a measure of the amount of material loss that each coated surface experienced, and the influence of time during impingement testing was taken into consideration. The surface morphology and the elemental composition of the coating before and after the erosion-corrosion test were examined using the SEM and EDS techniques. The results indicated that the coating over both spot-welded and plain stainless steel surfaces exhibited a similar degree of weight loss. However, the coating on the composite surface experienced a greater degree of weight loss. Microscopic observations of the fracture surfaces showed that the metal removal of the tested surface was concentrated around the unmelted and the semi-melted particles of the deposit.
Hot-Corrosion Performance of High-Velocity O*y-Fuel Sprayed Coatings
Abstrsct-Hot corrosion is a serious problem in boilers, gas turbines, internal combustion engines, and industrial waste incinerators. It consumes the materials at an unpredictably rapid rate. The use of protective coatings has been an answer to remedy the lack of high temperature surface stability of metals and alloys in harsh environments. Coating can be deposited by electric arc spray, physical vapour deposition, detonation spraying, llame spray, vacuum plasma spray, low pressure plasma spray, high velocity oxy fuel by sputtering or by evaporation. High-velocity oxy-fuel GfVOF) spraying is a new and rapidly developing technology in combating high-temperature corrosion. HVOF coatings have very low porosity, high hardness, high abrasive resistance, good wear resistance with a strong ability to resist hightemperature corrosion resistance. This study is done with the aim of putting together the performance capabilities and applications of HVOF process.
High velocity oxy-fuel (HVOF) thermal spray deposition of functionally graded coatings
Mahbub Hasan High Velocity Oxy Fuel Thermal Spray Deposition of Functionally Graded Coatings Phd Thesis Dublin City University, 2005
High Velocity Oxy-Fuel (HVOF) Thermal Spray Deposition of Functionally Graded Coatings Mahbub Hasan The present study investigates an innovative modification o f a HVOF (High Velocity Oxy-Fuel) thermal spray process to produce functionally graded thick coatings. In order to deposit thick coatings, certain problems have to be overcome. More specifically these problems include minimizing residual stresses, which cause shape distortion in assprayed components. Residual stresses in coatings also lead to adhesion loss, interlaminar debonding, cracking or buckling and are particularly high where there is a large property difference between the coating and the substrate. Graded coatings enable gradual variation o f the coating composition and/or microstructure, which offers the possibility o f reducing residual stress build-up in coatings. In order to spray such a coating, modification to a commercial powder feed hopper was required to enable it to deposit two powders simultaneously. This allows deposition of different layers o f coating with changing chemical compositions, without interrupting the spraying process. Various concepts for this modification were identified and one design was selected, having been validated through use o f a process model, which was developed using ANSYS Finite Element Analysis. The model simulates the flow of nitrogen gas and powder through the system, and verified the supply o f mixed composition powders. Based on this information a multi-powder feed unit was manufactured, commissioned and calibrated. Multi-layer coatings o f aluminium and tool-steel were sprayed onto aluminium substrates. The chemical composition of different layers of a five layer graded coating was determined using energy dispersive X-ray spectroscopy (EDS) to confirm functionality. Subsequently, various controlled parameters o f the HVOF spraying process were studied for this type o f coating using 33 factorial design o f experiments. Results were analysed in terms o f surface stress to deposition thickness ratio. The best combination o f spray parameters identified for deposition o f the mixed coating resembles those recommended for aluminium powder alone. It is proposed that this arises from the thermal properties o f the constituent powders. Different types o f aluminium/tool-steel functionally graded coatings were then deposited using the optimised set o f spray parameters, and considered using Clyne's analytical method o f stress analysis and Vickers hardness testing method. Coatings composed o f thicker layers resulted in much higher residual stress, but also improved hardness compared to thinner samples. It was found that if 5 layers o f graded material are sprayed, and the residual stress compared to that o f a traditional single layer (of the same thickness), an approximately 48 % reduction can be achieved. However this benefit is mitigated somewhat by the fact that applying these multi-layers reduces the hardness to by approximately 16 % compared to the traditional single layered deposit. Therefore an engineer must compromise between the stress and hardness when designing a functionally graded coating-substrate system.
Journal of Alloys and Compounds, 2009
Based on the merits of high-velocity oxy-fuel (HVOF) thermal spraying, hardness and cavitation erosion resistance of steel were improved with a Fe-Cr-Si-B (5.8 wt.% B) alloy coating applied to stainless steel (1Cr18Ni9Ti) substrate by HVOF thermal spraying. The microstructures and microhardness of the coating were investigated. It was found that the morphologies of the coating were of well-flattened splats (containing some un-melted borides), semi-molten particles, featureless structures and a small amount of pores. The average Vickers microhardness of the coating reached 9.9 GPa, about four times that of the substrate (2.8 GPa). From the substrate to coating, the indentation marks or the corresponding microhardness values changed gradually. The higher microhardness values of the substrate near the coating can be attributed to work hardening resulting from the impact of the melted or semi-molten particles and grit sand on the substrate. The microhardness of the well-flattened splats (10.8 GPa) is higher than that of the semi-molten particles (about 6.2 GPa) and the featureless regions (6.4 GPa), and the microhardness of the featureless regions is higher than that of the semi-melted particles. This suggests that the fully molten state of the feedstock can result in the formation of featureless structures and well-flattened splats (containing some un-melted borides) present high microhardness.
Materials Today: Proceedings, 2019
Chromium has excellent wear and corrosion properties with good lubrication and chemical resistance mainly used for decorative and practical applications. Nevertheless, the necessity to recognize replacements or to enhance the mechanical characteristics of chromium electroplating is of paramount importance mainly to overcome the environmental pollution and to enhance the fatigue strength of the substrate. The main reason for chromium coatings is to improve wear and corrosion properties of the component. But the main byproduct of this process is Cr + 6 (hexavalent chromium), that is hazardous to wellbeing of the surroundings. High Velocity Oxygen Fuel thermal spray coating (HVOF) is developed as an exceptional replacement for conventional hard chromium electroplating process. HVOF coatings possess improved hardness, wear and fatigue resistance in contrast to hard chromium coatings. An attempt has been made to conduct a survey to analyze the result of mechanical and tribological characteristics of HVOF coatings.
j m a t e r r e s t e c h n o l. 2 0 1 9;8(5):4253-4263 w w w. j m r t. c o m. b r High velocity oxygen fuel (HVOF) MCrAlY Thermal-barrier-coating (TBC) Bending test a b s t r a c t High-velocity oxygen fuel (HVOF) and flame spraying (FS) are alternative methods to thermal spraying processes to produce dense high-quality coatings. The aim of this study is to compare the microstructure and mechanical properties for HVOF and FS using a thermally sprayed bond coat NiCoCrAlY and CoNiCrAlY powders on an AISI 304 stainless steel substrate. The microstructure and composition of coatings were characterized by an X-ray Diffraction (XRD) analysis and Electron Microscopy (SEM) coupled to an Energy Dispersive Spectroscopy (EDS) detector. HVOF showed higher quality coatings compared to FS in terms of porosity and the presence of unfused particles for both employed powders. The mechanical properties and results indicated that the yield strength of the NiCoCrAlY (HVOF) coating was 1.4-folds FS, but the flexural bending modulus was almost the same. For the CoNiCrAlY powder, HVOF gave a higher yield strength and a higher flexural modulus than FS as the oxygen affinity of the CoNiCrAlY powder was lower than NiCoCrAlY given the high Co content in the former versus the latter. The results also indicated that hardness increased by about 83%, and by 58% for the NiCoCrAlY HVOF and FS coating alloys, and by 42% and 20% more for the CoNiCrAlY HVOF and FS coatings than the stainless steel substrate hardness, respectively.
Surface and Coatings Technology, 2020
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Surface and Coatings Technology, 2017
Ni-based coatings of the type Inconel 625 sprayed with high-kinetic spray processes are applied as protective coatings in many industrial fields where high corrosion resistance is required. High-Velocity Oxygen-Fuel (HVOF) and arc spray are common thermal spray methods used in the industry of power generation. Conversely, High-Velocity Air-Fuel (HVAF) and cold spray are nowadays technologies of rising interest because of their possibilities to create highly dense and low oxidised metallic coatings. This study aims to assess the effect of the different high-kinetic spray systems on chlorine-induced high temperature corrosion protection of Inconel 625 coatings. The coatings were exposed for 168 h to the test condition of 550°C under KCl salt deposits in 12% humidity air atmosphere. All the coatings provided effective protection to the substrate with the HVOF and arc sprayed coatings being the most resistant. The coatings were subjected to chlorine induced active oxidation and showed the typical layered structure of the external oxide deposit with chlorine detected at the coating/oxide interfaces. Signs of internal degradation were observed and were attributed to the penetration of chlorine through particle and splat boundaries. Chlorine was detected in some cases up to a depth of 200µm from the surface.